This invention relates generally to radiation apparatuses and methods, and in particular to multileaf collimators and methods of adjusting radiation beams useful in radiotherapy of diseases and other applications.
Radiation therapy is in common use in treating patients having tumors. One issue in radiation therapy is the movement of patient's internal organs caused by breathing. The internal organs' movement is significant enough that delivery of treatment dose to a fixed location may risk overdose to healthy organs and/or underdose to tumors. Conventional techniques include gating the radiation beam so that the beam is on only during stable and repeatable portions of the breathing cycle. Gating the beam on and off involves not treating during a large portion of the breathing cycle, therefore significantly increasing treatment time. This is compounded by the modulation factors of intensity-modulated radiation therapy (IMRT) that also increase the beam-off time. In arc therapy gating requires difficult starting and stopping the motion of a massive gantry, so gating is usually not implemented.
Another conventional technique includes moving the patient on a tracking couch so that the tumor remains stationary relative to a treatment field. Moving a patient using a tracking couch during treatment is generally deemed undesirable. Although the required patient acceleration may be slight, moving the patient introduces uncertainties in the position of soft tissues particularly if the patient reacts to the motion by tensing. The variations of motor noise and vibration may be disconcerting to the patient.